EP2318306A1 - Nanocomposites - Google Patents
NanocompositesInfo
- Publication number
- EP2318306A1 EP2318306A1 EP08794194A EP08794194A EP2318306A1 EP 2318306 A1 EP2318306 A1 EP 2318306A1 EP 08794194 A EP08794194 A EP 08794194A EP 08794194 A EP08794194 A EP 08794194A EP 2318306 A1 EP2318306 A1 EP 2318306A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- nanoparticles
- gold
- silver
- nanocomposite
- silver salt
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B7/00—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions
- C30B7/14—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions the crystallising materials being formed by chemical reactions in the solution
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/05—Metallic powder characterised by the size or surface area of the particles
- B22F1/054—Nanosized particles
- B22F1/0545—Dispersions or suspensions of nanosized particles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/16—Metallic particles coated with a non-metal
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/17—Metallic particles coated with metal
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/02—Elements
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/10—Inorganic compounds or compositions
- C30B29/46—Sulfur-, selenium- or tellurium-containing compounds
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/60—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape characterised by shape
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
- Y10T428/2991—Coated
Definitions
- the present invention relates to nanocomposites and to methods of making them.
- the nanoparticle may consist essentially of the silver salt.
- the nanoparticle may have a core-shell structure (i.e. may comprise a core and a shell surrounding said core), wherein the shell (or, in the case of a nanoparticle having more than one shell, the outermost shell) consists essentially of the silver salt.
- the silver salt may be capable of catalysing deposition of metallic gold on the surface thereof. It may be capable of catalysing the reduction of a gold salt (e.g. an Au(III) salt) to produce metallic gold. It may be a silver chalcogenide.
- the chalcogenide may be sulfide, selenide or telluride.
- the silver salt may be silver sulfide. It may be silver selenide. It may be silver telluride. It may be a mixture of any two or more of these.
- the nanoparticle may be substantially spherical.
- the nanocomposite particle may be substantially spherical.
- the region(s) of metallic gold may be approximately circular.
- the region of metallic gold, or each region of metallic gold independently, may have a diameter of about 1 to about 8nm.
- nanoparticle • a substantially spherical nanoparticle, said nanoparticle having a core-shell structure, wherein the shell consists essentially of silver sulfide, and
- a nanocomposite material comprising a plurality of nanocomposite particles, each of said nanocomposite particles being according to the first aspect.
- the nanocomposite material may consist essentially of said nanocomposite particles.
- the nanocomposite particles may have a mean diameter of about 5 to about 25nm. They may be substantially monodispersed. They may have a narrow particle size distribution.
- a process for making a nanocomposite material comprising:
- the precursor nanoparticles may consist essentially of metallic gold.
- the step of providing the precursor nanoparticles may comprise the step exposing an Au(III) salt to a reducing agent so as to form the nanoparticles.
- the reducing agent may be borohydride or some other reducing agent.
- the process may also comprise the step of transferring the gold precursor nanoparticles into an organic solvent prior to the step of forming the layer of the silver salt on the gold.
- the precursor nanoparticles may each comprise a core having the gold on a surface thereof.
- the core may comprise a material that is not gold.
- the step of providing the precursor nanoparticles may comprise heating the cores in the presence of Au(III) and an amine so as to deposit metallic gold on the surfaces of the cores.
- the cores may comprise, or may consist essentially of, metallic platinum, optionally together with a trace amount of silver.
- the process may comprise the step of heating Pt(acac) 2 in the presence of an amine and of a trace amount of silver so as to produce the cores.
- the silver salt may be silver sulfide.
- the step of forming the layer of the silver sulfide may comprise exposing the precursor nanoparticles to Ag(I) and elemental sulfur.
- the exposing may be in the presence of an alkyl amine. It may be conducted in an organic solvent.
- the step of aging may comprise maintaining the coated nanoparticles in a solvent, e.g. an organic solvent, for sufficient time for the gold of each coated nanoparticle to diffuse through layer of the silver salt to the surface of said coated nanoparticle.
- a solvent e.g. an organic solvent
- the precursor nanoparticles may have a mean diameter of about 3 to about 25nm. They may be substantially monodispersed. They may have a narrow particle size distribution.
- a process for making a nanocomposite material comprising:
- a process for making a nanocomposite material comprising:
- the silver salt may be silver sulfide.
- the step of providing the nanoparticles may comprise reacting an Ag(I) salt with elemental sulfur so as to form the nanoparticles.
- the exposing may be in the presence of an amine.
- the nanoparticles may be provided in an organic solvent. They may be produced in the organic solvent.
- the step of depositing metallic gold may comprise exposing the nanoparticles to a solution of Au(III) in the presence of an amine. This step may be conducted in an organic solvent.
- a process for forming a making a nanocomposite material comprising:
- the invention also provides a nanocomposite material made by the process of either the third or the fourth aspect of the invention.
- a nanocomposite material comprising nanocomposite particles according to the first aspect, or of a nanocomposite material according to the second aspect, or of a nanocomposite material made by the process of the third or the fourth aspect, as a catalyst, or for making an optical or an electronic device.
- the aqueous solution may comprise an alcohol. It may comprise a water miscible alcohol, e.g. ethanol.
- the step of providing the aqueous solution may comprise combining a solution of the silver salt in water with a solution of the alkyl amine in the alcohol.
- the alkyl amine may be a primary alkyl amine. It may be a long chain alkyl amine. It may be a C8 to Cl 8 alkyl amine e.g. dodecylamine or a mixture of C8 to Cl 8 alkyl amines.
- the silver salt may be silver nitrate.
- the organic solvent may have low miscibility with water. It may be a hydrocarbon solvent. It may be an aromatic solvent. It may for example be benzene, toluene or xylene. It may be a mixture of individual solvents.
- the silver compound may be silver sulfide.
- the step of precipitation may comprise exposing the organic solution to elemental sulfur. This may comprise combining the organic solution with an organic solution of the sulfur.
- the solvent for the organic solution of sulfur may be miscible with the organic solvent of the organic solution. It may be the same as or may be different to the organic solvent of the organic solution.
- the silver compound may precipitate as a suspension or a dispersion.
- the dispersion or suspension may be stable.
- the process may be conducted at room temperature. It may be conducted at about 15 to about 25 0 C.
- the the step of extracting may result in at least about 95% transfer of silver ions from the aqueous solution.
- Figure 1 shows (a, b) TEM images, (c) HRTEM image, and (d) SAED pattern of the Ag 2 S nanocrystals.
- Figure 2 shows (a) TEM and (b) HRTEM images of Au/Ag 2 S heterogeneous nanostructures.
- (c) TEM and (d) HRTEM images of Ag 2 S-Au shell-core nanoparticles (Ag 2 SiAu molar ratio 2:1).
- TEM and (h) HRTEM images of Ag 2 S-Au shell-core nanoparticles (Ag 2 S:Au molar ratio 2:1) after 108 h of aging.
- Figure 3 shows UV-visible spectra of Ag 2 S, Au. and core-shell Au(SAg 2 S nanocrystals with different molar ratio of Ag?S to Au.
- Figure 4 is a diagrammatic representation of the formation of silver sulfide/gold nanocomposites .
- Figure 5 shows an XRD pattern of the as-prepared Ag 2 S nanocrystals.
- Figure 7 shows EDX analysis of the Au/Ag 2 S heterodimers.
- Figure 8 shows XPS spectra of the Au/Ag 2 S heterodimers.
- Figure 9 illustrates diffusion of Au from the core to the surface of core-shell Au@Ag 2 S nanocrystals.
- Figure 10 is a schematic of the synthesis of semiconductor-metal nanocomposite based on the diffusion of Au in Ag 2 S.
- Figure 11 shows (a,c) TEM and (b,d) HRTEM images of (a,b) core-shell-shell
- Figure 12 illustrates Ostwald ripening observed during the diffusion of Au in Ag 2 S.
- Au diffuses homogeneously in Ag 2 S in all directions, but then evolves as growing nanocrystals on the Ag 2 S surface due to Ostwald ripening.
- Figure 13 shows (a) TEM and (b) HRTEM images of 5-nm Au seeds transferred from water to toluene.
- Figure 14 shows (a) TEM and (b) HRTEM images of 4-nm Pt nanoparticles synthesized in oleylamine.
- Figure 15 shows (a) TEM and (b) HRTEM images of core-shell Pt@Au nanoparticles synthesized in oleylamine by seed-mediated growth method.
- Figure 16 shows a TEM image of Ag 2 S nanocrystals (in grey tone) synthesized in the presence of Pt seeds (in a darker shade). Ag 2 S does not grow on the existing Pt seeds, but form separate particles in the colloid instead.
- Figure 17 shows STEM analyses showing the confinement of Pt and Au in the core and on the surface, respectively, of Pt@Ag 2 S-Au nanocomposite.
- A@B indicates a core-shell structure in which the core consists essentially of A and the shell consists essentially of B. Consequently the terminology A@B@C indicates a core-shell-shell structure in which a core consisting essentially of A is surrounded by a shell consisting essentially of B, which is in turn surrounded by a further shell consisting essentially of C.
- the present invention provides a nanocomposite particle comprising a nanoparticle having a surface comprising a silver salt, and at least one region of metallic gold on said surface.
- the nanoparticle and the nanocomposite particle may each, independently, have a diameter of about 5 to about 25nm or about 5 to 20, 5 to 15, 10 to 25, 15 to 25 or 10 to 20nm, e.g. about 5, 10, 15, 20 or 25nm, provided that the diameter of the nanoparticle is less than or equal to that of the nanocomposite particle.
- the nanoparticle and the nanocomposite particle may, independently, be spherical, approximately spherical, oblate spherical, ovoid, polyhedral or some other shape.
- the region, or each region independently, may be round, oval, polygonal or irregular, or some other shape. It (they independently) may be about 1 to about 8nm in diameter, or about 1 to 5, 1 to 3, 3 to 8, 5 to 8 or 2 to 6nm, e.g. about 1, 2, 3, 4, 5, 6, 7 or 8nm in diameter.
- the diameter of the, or each, region should be smaller than that of the nanoparticle.
- the nanoparticle is completely coated in the gold (i.e.
- the thickness of the region(s) of gold may be less than about 2nm, or less than 1, 0.5 or 0.2nm, or may be about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5 or 2nm thick. It may be about 1 to 20 atoms thick, or 1 to 10, 1 to 5, 5 to 20, 10 to 20 or 5 to 10 atoms thick, e.g.
- the gold may be at least about 90% pure (on a mole basis) or at least about 95, 99, 99.5 or 99.9% pure.
- the nanoparticle consists essentially of the silver salt.
- the silver salt may be at least about 90% pure on a mole basis, or at least about 95 or 99% pure. It may consist essentially of a mixture of silver salts, in which case at least about 90% (or at least about 95 or 99%) of the metal content of the mixture may be silver on a mole basis.
- the silver salt may have low or negligible water solubility. It may have low or negligible solubility in organic solvents, particularly in the organic solvent(s) (e.g. toluene) used in making it or in using it to make the nanocomposite particles.
- the nanoparticle has a core-shell structure.
- the shell may consist essentially of, or may comprise, the silver salt.
- the core may have a diameter of about 1 to about IOnm, or about 1 to 5, 5 to 10, 2 to 10, 2 to 5 or 3 to 5nm, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9 or IOnm. It may comprise, or consist essentially of, metallic platinum or metallic palladium or a mixture of these.
- the nanoparticle may be a Pt@Ag 2 S nanoparticle.
- a plurality of the cores (used for making a nanocomposite material as described herein) may have a mean particle diameter as described above for the particle diameter.
- the cores may have a narrow particle size distribution.
- the shell of the core shell particle may be about 1 to about IOnm in thickness, or about 1 to 5, 1 to 2, 2 to 10, 5 to 10, 2 to 8 or 2 to 5nm, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9 or IOnm. In the case of a plurality of cores, these may be mean values.
- the inventors have found that metallic gold (Au(O)) is capable of diffusing through a layer of a silver salt to a surface thereof. They have used this surprising phenomenon in order to make a nanocomposite material comprising nanocomposite particles as described above.
- the process comprises forming a layer of a silver salt on the surfaces of a plurality of precursor nanoparticles, said surfaces comprising metallic gold. Aging of the resulting coated nanoparticles allows the gold to at least partially diffuse through the layer of the silver salt to the surface of said coated nanoparticle so as to form one or more regions of metallic gold on the surfaces.
- the inventors have further found that an Ostwald ripening phenomenon occurs such that larger regions of gold on the surface of a nanoparticle can grow over time at the expense of smaller regions.
- nanocomposite particle having only a single gold region on the surface.
- more than one gold region may be present on the surface, and these may have different sizes or may be approximately the same size.
- Different nanocomposite particles in a nanocomposite material may have different numbers and/or sizes of regions of gold on their surfaces.
- the precursor nanoparticles used in making the nanocomposite material may have a mean diameter of about 3 to about 25nm or about 3 to 15, 3 to 10, 3 to 5, 5 to 25, 5 to 20, 5 to 15, 10 to 25, 15 to 25 or 10 to 20nm, e.g. about 3, 4, 5, 6, 7, 8, 9, 10, 15, 20 or 25nm.
- the layer of silver salt formed on the surface of the precursor nanoparticles may be about 1 to about IOnm in thickness, or about 1 to 5, 1 to 2, 2 to 10, 5 to 10, 2 to 8 or 2 to 5nm, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9 or IOnm.
- the precursor nanoparticles used in the process may consist essentially of metallic gold. They may have a purity of at least about 90% pure (on a mole basis) or at least about 95, 99, 99.5 or 99.9%. Alternatively they may comprise a gold alloy or some other gold-containing mixture.
- Suitable gold precursor nanoparticles for use in the process may be made by reducing an Au(III) salt with a reducing agent so as to form the precursor nanoparticles. This may be conducted in an aqueous medium, in which case the reducing agent should be a water compatible reducing agent such as borohydride. In this case also, the Au(III) salt should be water soluble. It may for example be AuCl 3 .
- a stabilising agent for the gold precursor nanoparticles may also be present.
- Suitable stabilising agents include citrate, PVP (polyvinylpyrrolidone) or surfactants.
- Suitable surfactants may be non-ionic surfactants such as Triton X-100 (t-octylphenoxypolyethoxyethanol).
- Stabilisers in general stabilise the nanoparticles by adsorbing on the surface so as to prevent or inhibit aggregation of the nanoparticles by electrostatic interaction.
- the process may also comprise the step of transferring the gold precursor nanoparticles into an organic solvent prior to the step of forming the layer of the silver salt on the gold.
- the transfer may involve mixing the aqueous mixture containing the gold precursor nanoparticles with a water-miscible organic solvent containing a transfer agent.
- the transfer agent may comprise an alkyl amine.
- the water-miscible organic solvent may suitably be a short chain alcohol such as ethanol or methanol, or other polar solvent such as acetone.
- the alkyl amine may be a long chain alkyl amine. It may be a primary amine.
- the alkyl group on the amine may be about C6 to about C20, or about C6 to C 12, C12 to C20, C12 to C16, C8 to C14 or ClO to C14, e.g.
- the alkyl group may be straight chain. It may be saturated. It may be unsaturated. It may comprise one or more double and/or triple bonds (i.e. it may be an alkenyl or alkynyl or alkenynyl group). It may be a mixture of such alkyl amines.
- the amine may be a secondary or tertiary amine, or may be a quaternary ammonium salt.
- the amine (or ammonium salt) should have an amine group which is capable of binding to (or associating with) the nanoparticle, and a non-polar tail which facilitates dispersion of the particle in a non-polar solvent.
- the alkyl groups on a secondary or tertiary amine or an ammonium salt may each, independently, be as described above.
- a mixture of the amines and/or ammonium salts described above may be used.
- An alternative transfer agent comprises dipotassium bis(p- sulfonatophenyl)phenylphosphane dehydrate (BSPP). Extraction of the resulting aqueous/organic mixture with a suitable organic extractant transfers the gold precursor nanoparticles to the organic extractant.
- the organic extractant may be a low polarity or non-polar organic solvent. It may be an aromatic solvent such as benzene, toluene, xylene etc. It may be a mixture of solvents comprising one or more of these.
- core-shell precursor nanoparticles in which the shell comprises gold may be used.
- the precursor nanoparticles each comprise a core having the gold on a surface thereof.
- the core may comprise a material that is not gold. It may for example comprise platinum or palladium or a mixture of these.
- a suitable process for making the cores comprises reducing a salt or complex of a metal.
- a suitable metal for the core is platinum.
- the precursor to the metal cores may be Pt(acac) 2 . This may be reduced to nanoparticulate platinum metal in the form of nanosized cores by heating in the presence of an amine (optionally in the absence of further solvent.
- a trace amount of a silver salt is added in order to produce the desired spherical cores.
- Suitable amines are as described above in the synthesis of the gold precursor nanoparticles.
- the reaction is preferably conducted under an inert atmosphere, e.g. helium, neon, argon, nitrogen or a mixture of these.
- Suitable temperatures are about 120 to 200 0 C, or about 140 to 200, 160 to 200, 120 to 160 or 140 to 18O 0 C, e.g. about 120, 130, 140, 150, 160, 170, 180, 190 or 200 0 C.
- a shell of gold may be then deposited on the surfaces of the cores in order to form the core-shell precursor nanoparticles.
- the platinum cores in amine may be treated with a gold compound so as to form a gold shell on the cores, thereby forming the core-shell precursor nanoparticles Pt@Au.
- the amine may be sufficient to convert (reduce) the gold compound to metallic gold (Au(O)).
- the gold compound may be a gold salt, such as a gold (III) salt, for example AuCl 3 or AuBr 3 .
- the reaction is conducted under an inert atmosphere as described above for formation of the core.
- a suitable reaction temperature for deposition of gold on the core to form a shell is about 80 to 12O 0 C, or about 80 to 100, 100 to 120 or 90 to HO 0 C, e.g. about 80, 85, 90, 95, 100, 105, 110, 115 or 12O 0 C.
- the reaction mixture may be cooled to the desired shell formation temperature while maintaining the same atmosphere over the mixture, and the gold compound added.
- the core-shell precursor nanoparticles may be purified. This may for example comprise one or more of precipitating, washing, centrifuging or other suitable techniques. They may then be suspended in an organic solvent for subsequent elaboration.
- the organic solvent may be a low polarity or non-polar organic solvent. It may be an aromatic solvent such as benzene, toluene, xylene etc. It may be a mixture of solvents comprising one or more of these.
- the process may then comprise forming a layer of a silver salt on the surface of the precursor nanoparticles.
- This may comprise converting the silver ions in solution to a form in which they are substantially insoluble in the reaction medium (which is commonly an organic solvent such as toluene).
- the reaction medium which is commonly an organic solvent such as toluene.
- it may comprise forming a layer of an insoluble silver salt on the surface of the precursor nanoparticles, where the insoluble silver salt is insoluble in the reaction medium. It may comprise precipitating a layer of the insoluble silver salt on the surface of the precursor nanoparticles.
- the silver salt is silver sulfide.
- the step of forming the layer of the silver sulfide may comprise exposing the precursor nanoparticles to Ag(I) and elemental sulfur.
- an organic solvent such as the low polarity solvent described above. It may be necessary to transfer the precursor nanoparticles into the organic solvent, as described above. In this case it is also necessary to provide the Ag(I) in an organic solvent (optionally the same organic solvent in which the precursor nanoparticles are provided). This may be accomplished in a similar manner as described above for transfer of the gold precursor nanoparticles into an organic solvent.
- aqueous Ag(I) may be mixed with a water miscible organic solvent (e.g. ethanol) and an amine (as described previously). The resulting solution can then be extracted with an organic extractant so as to provide a solution of Ag(I) in the extractant (i.e. an organic Ag(I) solution).
- the organic extractant should preferably be the same as, or at least miscible with, the organic solvent in which the gold precursor nanoparticles are provided.
- Combination of the gold precursor nanoparticles in the organic solvent with the organic Ag(I) solution, and treatment of the resulting mixture with elemental sulfur results in conversion of the Ag(I) to Ag 2 S, which forms as a layer on the precursor nanoparticles so as to generate the coated nanoparticles.
- amine present as a result of transfer of the Ag(I) and/or the gold precursor nanoparticles into organic media may reduce, or catalyse the reduction of, the elemental sulfur to S 2" , which can then combine with the Ag(I) ions to form Ag 2 S.
- the reaction is preferably conducted with vigorous agitation in order to ensure exposure of all reagents to each other and to prevent agglomeration which would inhibit the layer formation.
- the layer formation may be conducted at room temperature, or at some other suitable temperature, e.g. about 0 to about 100 0 C, or about 0 to 50, 0 to 25, 0 to 10, 10 to 100, 20 to 100, 50 to 100, 15 to 50, 15 to 30 or 20 to 25 0 C, e.g. about 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 0 C.
- aging of the resulting coated nanoparticles can allow metallic gold to diffuse or migrate through the silver compound so as to form the nanocomposite particles.
- the step of aging may simply comprise maintaining the coated nanoparticles in a solvent for sufficient time for the gold of each coated nanoparticle to diffuse through layer of the silver salt to the surface of said coated nanoparticle. This may take between about 6 and about 48 hours, or between about 6 and 24, 6 and 12, 12 and 48, 24 and 48, 12 and 36 or 18 and 30 hours, e.g. about 6, 12, 18, 24, 30, 36, 42 or 48 hours.
- the time may depend on the thickness of the layer of silver compound over the gold in the coated nanoparticles, and may also depend on the temperature of the aging.
- the aging may be conducted at room temperature, or at some other suitable temperature, e.g. about 0 to about 100 0 C, or about 0 to 50, 0 to 25, 0 to 10, 10 to 100, 20 to 100, 50 to 100, 15 to 50, 15 to 30 or 20 to 25 0 C, e.g. about 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 0 C.
- suitable temperature e.g. about 0 to about 100 0 C, or about 0 to 50, 0 to 25, 0 to 10, 10 to 100, 20 to 100, 50 to 100, 15 to 50, 15 to 30 or 20 to 25 0 C, e.g. about 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 0 C.
- a second process for making the nanocomposite particles involves direct precipitation of metallic gold onto nanoparticles having a silver salt on their surface.
- a suitable silver salt is silver sulfide.
- the nanoparticles may be made by reacting an Ag(I) salt with elemental sulfur so as to form the nanoparticles.
- the process for making the Ag 2 S nanoparticles may be similar to the process described above for deposition of a layer of silver sulfide on the surface of gold precursor nanoparticles, however with the omission in this case of the gold precursor nanoparticles.
- aqueous Ag(I) having a water miscible organic solvent and an amine is extracted into an organic extractant, and the resulting organic Ag(I) solution is treated with elemental sulfur.
- the nanoparticles may comprise or consist essentially of the silver salt. Alternatively they may comprise a core that is not the silver salt, with a shell of the silver salt surrounding the core. It should be noted that deposition of a layer of silver sulfide on the surface of platinum cores (similar to the deposition of gold on such cores as described earlier) could not be achieved by reaction of sulfur with silver (I) in the presence of platinum cores.
- the deposition of metallic gold on the nanoparticles having a silver salt surface may comprise exposing the nanoparticles to a solution of Au(III) in the presence of an amine. As for previous reactions this is preferably conducted in an organic medium. Thus Au(III) could be transferred into an organic extractant in the same manner as described earlier for transfer of Ag(I) and of gold precursor nanoparticles. Simply combining the organic Au(III) solution and the nanoparticles in an organic solvent leads to formation of metallic gold on the nanoparticle surfaces, leading directly to the nanocomposite particles. It is thought that the amine (described in detail earlier) is sufficient to reduce Au(III) to Au(O), or to catalyse that reduction, so as to form the metallic gold on the nanoparticle surfaces.
- the reaction may be conducted at room temperature, or at some other suitable temperature, e.g. about 0 to about 100 0 C, or about 0 to 50, 0 to 25, 0 to 10, 10 to 100, 20 to 100, 50 to 100, 15 to 50, 15 to 30 or 20 to 25 0 C, e.g. about 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 0 C. It may take about 0.5 to about 2 hours, or about 0.5 to 1, 1 to 2 or 0.7 to 1.5 hours, e.g. about 30 or 45 minutes, or about 1, 1.25, 1.5, 1.75 or 2 hours. The time may depend in part on the temperature used. It is thought that the silver salt on the surface of the nanoparticles may catalyse the amine reduction of the gold (III) so as to form the gold preferentially on the nanoparticle surfaces.
- nanocomposite materials described herein may find applications as a catalyst, or for making optical or electronic devices.
- the nanocomposite materials have been tested as catalysts in three-component coupling reactions, and displayed excellent catalytic activity. A representative reaction is shown below:
- the Ag 2 S shell may be used to modulate the optical properties of nanoparticulate gold.
- the nanocomposite material described herein may be used in optical or electronic devices.
- the present invention also provides a process for producing nanoparticles of a silver compound.
- the process provides a suspension or dispersion of the silver compound in an organic medium.
- an aqueous solution comprising a silver salt and an alkyl amine is extracted with an organic solvent so as to transfer the silver salt to the organic solvent.
- the resulting organic solution contains silver ions which are then precipitated in the organic solution as nanoparticles of the silver compound.
- the aqueous solution may comprise an alcohol or some other water-miscible organic solvent, e.g. a water miscible alcohol. Suitable examples include methanol, ethanol, propanol, isopropanol, acetone and tetrahydrofuran.
- a solution of the silver salt in water may therefore be combined with the alkyl amine and the alcohol to provide the aqueous solution used in the process.
- the alkyl amine may be a primary alkyl amine. It may be a long chain alkyl amine. It may be a C8 to Cl 8 alkyl amine e.g. dodecylamine or a mixture of C8 to Cl 8 alkyl amines. Suitable amines are the same as those used in transferring gold particles into organic media, and have been described earlier in this specification.
- the silver salt may be any water soluble silver salt. It may be a silver (I) salt. It may be silver nitrate, or it may be silver fluoride or it may be silver acetate or it may be a mixture of soluble silver salts.
- the organic solvent may have low miscibility with water. It may be a hydrocarbon solvent. It may be an aromatic solvent. It may for example be benzene, toluene or xylene. It may be a mixture of any two or more of these, or it may be a mixture of any one of these with some other solvent, e.g. with one or more other solvents having low water miscibility.
- Transfer of silver ions from aqueous to organic media may be facilitated by the presence of the alkyl amine. Thus the amine may associate with the silver ions, and the hydrophobic tail of the amine may facilitate transfer of the resulting silver ion-amine association to the organic solvent.
- the presence of an organic solvent such as an alcohol in the aqueous solution may facilitate the dissolution of the amine (or of the amine-silver ion association) in the aqueous solution prior to the extraction.
- the transfer of silver from aqueous to organic media may be efficient. It may be at least about 90% efficient, or at least about 95, 96, 97, 98 or 99% efficient. It will be apparent that the above process may be conveniently used for transfer from aqueous to organic media of species that are capable of associating with, or forming a complex with, an amine, hi the present specification the examples of transfer of silver ions and of gold nanoparticles are presented, however other species may also be transferred at room temperature using an analogous protocol.
- the extraction step described above results in an organic solution of a silver salt, in particular of a water soluble silver salt.
- the silver in said organic solution may be associated with the amine.
- the proportions of water, water miscible organic solvent and organic solvent with low miscibility with water should be such that during the extraction step of the above process, an aqueous phase and a non-aqueous phase separate, wherein the non-aqueous phase contains the majority of the silver ions.
- the silver compound formed from the silver ions in the organic solvent may be silver sulfide or it may be some other silver salt (e.g. silver (I) salt) which is substantially insoluble in the organic solvent (optionally also substantially insoluble in water).
- the silver compound may be formed by combination of the silver ions in the organic solvent with a suitable counterion which converts the silver ions to an insoluble silver compound.
- the step of precipitation may comprise exposing the organic solution to elemental sulfur. It is thought that this reaction proceeds by way of reduction of the sulfur to sulfide ions, which can then condense with the silver ions to form silver sulfide nanoparticles. The reduction may involve reaction with, or catalysis by, the amine.
- the silver compound may precipitate as a suspension or a dispersion.
- the particles of the silver compound that are produced by the process may have a mean diameter of about 3 to about 25nm or about 3 to 15, 3 to 10, 3 to 5, 5 to 25, 5 to 20, 5 to 15, 10 to 25, 15 to 25 or 10 to 20nm, e.g. about 3, 4, 5, 6, 7, 8, 9, 10, 15, 20 or 25nm.
- the process may be conducted at room temperature. It may be conducted at about 15 to about 25 0 C, or about 15 to 20, 20 to 25 or 18 to 23 0 C, e.g. about 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 or 25 0 C. In some cases it may be conducted at some other temperature.
- the invention also provides a suspension or dispersion of nanoparticles of a silver compound in an organic solvent.
- the suspension or dispersion may be made by the process described above.
- the silver compound and the organic solvent may be as described above.
- the suspension or dispersion may be stable. It may be stable for at least about 1 day, or at least about 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14 days. It may be stable in that the particles do not settle over that period of time.
- the present describes a room-temperature approach to synthesize Ag 2 S nanocrystals (nanoparticles) in toluene.
- the protocol involved firstly transferring Ag(I) ions from aqueous solution into toluene using a method mediated by ethanol and dodecylamine, and then reacting with elemental sulfur in toluene at room temperature to form the Ag 2 S nanocrystals.
- nanocomposites were formed between gold and Ag 2 S through the heterogeneous deposition of gold on the Ag 2 S nanocrystals or by the homogeneous growth of Ag 2 S on Au nanocrystals.
- the latter approach produced Ag 2 S-Au shell-core structures, which induced a red-shift of the surface plasmon resonance (SPR) of gold nanocrystals.
- SPR surface plasmon resonance
- BSPP dipotassium bis(p-sulfonatophenyl)phenylphosphane dehydrate
- the present approach allows for the synthesis of Ag 2 S nanocrystals with a narrow size distribution at room temperature.
- the protocol used to transfer Ag(I) ions from water to toluene may be extended to synthesize Ag 2 S and gold nanocomposites, including the heterogeneous deposition of gold on Ag 2 S nanocrystals and the homogeneous growth of Ag 2 S on gold nanocrystals.
- the latter produced Ag 2 S-Au shell-core structures.
- This technology provides a simple and convenient route to prepare Ag 2 S nanocrystals and their nanocomposites with gold.
- the resulting materials are of interest for optical, electronic, energy, catalytic and biological applications.
- the present disclosure also describes the diffusion of gold through Ag 2 S from the core of core shell nanoparticles to the surface, giving rise to novel Ag 2 S-Au heterodimers (nanocomposites). This phenomenon may be used to synthesize complex semiconductor- metal nanocomposites which might not be obtainable by direct synthesis. Specifically, the synthesis of heterogeneous nanocomposites of core-shell Pt@Ag 2 S and of Au nanoparticles based on the diffusion of Au in Ag 2 S in core-shell-shell Pt@Au@Ag 2 S nanoparticles is described.
- This diffusion process provides a new strategy for synthesizing semiconductor- metal hybrids or for metal doping in semiconductor nanocrystals.
- the resulting materials are of interest for optical, electronic, electrochemical, energy, catalytic and biological applications.
- Example 1 Room-temperature synthesis of nanocrystalline silver sulfide and its nanocomposites with gold.
- the present disclosure describes nanocomposites formed between gold and Ag 2 S by the heterogeneous deposition of gold on Ag 2 S nanocrystals, and by the homogeneous growth of Ag 2 S on gold nanocrystals.
- the latter produced shell-core Ag 2 S-Au nanostructures, which induced the red-shift of the surface plasmon resonance (SPR) of Au nanocrystals.
- SPR surface plasmon resonance
- the thickness of the Ag 2 S shell could be controlled by varying the Ag 2 S: Au molar ratio in the synthesis.
- Figures 2e and f illustrate the Ag 2 S-Au shell-core nanocrystals synthesized at Ag 2 SiAu molar ratios of 1 :2 and 1 :1.
- the thickness Of Ag 2 S shell could be varied as shown b ⁇ comparing Figures 2c. e and f.
- Ag 2 S-Au shell-core nanoparticles retained the optical properties of Au nanocrystals despite the presence of the Ag 2 S shell (see Figure 3).
- the absorption peaks at 567 run, 576 nm and 593 nm were attributed to the surface plasmon resonance (SPR) of gold cores.
- SPR surface plasmon resonance
- the large red-shift of the gold surface plasmon band in these shell-core nanoparticles relative to the pure gold nanocrystals could be attributed to the presence of the Ag 2 S shell.
- the SPR peak of the gold cores could be tuned by the thickness of the Ag 2 S shell.
- the inventors have demonstrated a room-temperature synthesis for Ag 2 S nanocrystals and their nanocompsites with gold.
- Gold could be deposited only at a single site on each Ag 2 S seed nanocrystal.
- Ag 2 S could grow homogeneously on Au seed nanocrystals, resulting in shell-core Ag 2 S-Au nanoparticles, which still possessed the optical properties of Au nanocrystals.
- This facile synthesis could be employed towards fabricating a variety of nanocomposites with interesting structures and tailored functionalities. The formation of the nanocomposites is illustrated in Fig. 4.
- Phase transfer of noble metal ions from water to toluene Phase transfer of noble metal ions from water to toluene.
- 50 mL of 1 mM of aqueous metal salt solution AgNO 3 or HAuCl 4
- 50 mL of toluene was added, and stirred for another minute.
- Phase transfer of metal ions from water to toluene occurred rapidly and completely, as illustrated by the complete bleaching of the colour in the aqueous phase.
- the metal ion concentration in toluene assuming complete transfer of the ions from water was 1 mM.
- ICP-AES Inductively coupled plasma-atomic emission spectrophotometry
- the BSPP-stabilized Au hydrosol was mixed with 20 mL of ethanol containing 0.4 mL of dodecylamine. After 3 min of stirring, 20 mL of toluene were added and stirred for another minute. ICP-AES analysis showed that this phase transfer efficiency was about 100%.
- the TEM and HRTEM images of Au nanoparticles after phase transfer are shown in Figure 6.
- Example 2 Synthesis of Complex Semiconductor-Metal Nanocomposites Based on the Diffusion of Au in Ag 2 S Nanocrystals from Core to Surface
- the driving force for the diffusion of Au in Ag 2 S from core to surface could be similar to that underlying the Kirkendall effect, which has been used in the past to form hollow particles. Due to the relatively high surface-to-volume ratio, the diffusion of Au in core-shell Au@Ag 2 S nanocrystals from core to surface could be achieved so that the system decreased its chemical potential and reduced its Gibbs free energy.
- Core-shell Pt@Au nanoparticles were prepared using seed-mediated growth method, and next coated with Ag 2 S (see Figure 10). Gold then diffused to the surface of Ag 2 S, resulting in a heterogeneous hybrid of core-shell Pt@Ag 2 S and Au nanoparticles, labeled as Pt@Ag 2 S-Au (see Figure 1 1). It should be noted that core-shell Pt@Ag 2 S nanoparticles could not be synthesized directly; Ag 2 S nanocrystals were formed independently in solution in the presence of Pt seeds ( Figure 16).
- Ostwald ripening was observed during the characterization of the heterostructured nanocomposites. Ostwald ripening is a phenomenon whereby particles larger than a critical size grow at the expense of smaller particles due to their relative stabilization by the surface energy term.
- Figure 12 shows the TEM images of four nanocomposites captured over a period of 20s. Evolution of gold patches or regions on the surface of the nanocomposites was clearly observed. The ripening observed in TEM might not exactly represent the case in solution since the electron beam might have affected the process. However, this observation suggested a reason why the diffusion process did not lead to a homogeneous distribution of gold on the particle surface. Initially, gold atoms might have diffused in all directions within Ag 2 S. However, nanoparticles of gold were then formed on the Ag 2 S surface and grew steadily due to Ostwald ripening.
- 5-nm citrate- protected Au nanoparticles were prepared by the NaBH 4 reduction of HAuCl 4 - First, 20 ml of aqueous HAuCl 4 solution (1 mM) were mixed with 1.6 ml of aqueous sodium citrate solution (40 mM). Next, 0.5 ml of aqueous NaBH 4 solution (100 mM) was added dropwise under vigorous stirring, giving rise to a red Au hydrosol. The gold hydrosol was used after aging for 24 h to decompose the residual NaBH 4 . Gold nanoparticles were transferred from water to toluene following the approach used for the phase transfer of Ag(I) ions.
- the citrate-stabilized gold hydrosol was mixed with 20 ml of ethanol containing 0.4 ml of dodecylamine. After 3 min of stirring, 20 ml of toluene were added and stirred for another minute. ICP-AES analysis showed that the phase transfer efficiency was about 100%.
- the TEM and HRTEM images of gold nanoparticles after phase transfer are shown in Figure 13.
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TWI520766B (en) * | 2012-08-27 | 2016-02-11 | 國立清華大學 | Nanoparticle phase transferring method |
US9040158B2 (en) * | 2012-09-18 | 2015-05-26 | Uchicago Argonne Llc | Generic approach for synthesizing asymmetric nanoparticles and nanoassemblies |
CN108806836B (en) * | 2013-04-05 | 2020-11-13 | 苏州诺菲纳米科技有限公司 | Transparent conductive electrodes with fused metal nanowires, their structural design and methods of making the same |
US10059585B2 (en) * | 2016-06-28 | 2018-08-28 | Nanoco Technologies Ltd. | Formation of 2D flakes from chemical cutting of prefabricated nanoparticles and van der Waals heterostructure devices made using the same |
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KR102484809B1 (en) | 2018-10-02 | 2023-01-05 | 재팬 사이언스 앤드 테크놀로지 에이전시 | Heteroepitaxial structure and method for manufacturing the same, metal laminate including the heteroepitaxial structure and method for manufacturing the same, and nanogap electrode and method for manufacturing the nanogap electrode |
US11053135B2 (en) | 2019-05-03 | 2021-07-06 | Aegis Technology Inc. | Scalable process for manufacturing iron cobalt nanoparticles with high magnetic moment |
CN115609001B (en) * | 2022-07-15 | 2023-10-10 | 西北工业大学 | Method for preparing functionalized gold nanoparticles by using alkyne compounds |
CN116890119B (en) * | 2023-07-12 | 2024-01-23 | 山东第一医科大学(山东省医学科学院) | One-step synthesis of Ag/Ag 2 S Janus heterojunction and application thereof |
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